Histologic, immunohistochemical and ultrastructural studies were made on myocardial specimens obtained from 11 patients with AL amyloidosis to evaluate the clinicopathologic correlations in this disorder. The study demonstrated that myocardial biopsy serves to: 1)establish the diagnosis of cardiac amyloidosis; 2)characterize immunohistochemically the proteins in the amyloid fibrils; 3)assess the degree of myocyte damage and atrophy.